1. Field of the Invention
The present invention relates to a heat treatment method and a heat treatment apparatus for performing a post-exposure bake process on a thin plate-like precision electronic substrate such as a semiconductor wafer and a glass substrate for a liquid crystal display device (hereinafter referred to simply as a “substrate”).
2. Description of the Background Art
Products of semiconductor devices, liquid crystal display devices and the like are fabricated by performing a series of processes including cleaning, resist coating, exposure, development, etching, interlayer insulation film formation, heat treatment, dicing and the like on the aforementioned substrate. A substrate processing apparatus which performs, among the aforementioned processes, a resist coating process on a substrate to transfer the substrate to an exposure unit and which receives an exposed substrate from the exposure unit to perform a development process on the exposed substrate is widely used as what is called a coater-and-developer. U.S. Patent Application Publication No. 2009/060686 discloses an example of such a substrate processing apparatus.
For a coater-and-developer adaptable to an exposure unit which uses ArF and KrF excimer laser, it is essential to form a film of chemically amplified resist on a substrate to transfer the substrate with the film formed thereon to the exposure unit and to perform a post-exposure bake (PEB) process on an exposed substrate. U.S. Patent Application Publication No. 2009/060686 discloses the execution of a post-exposure bake process which causes a reaction such as crosslinking, deprotection or decomposition and the like of resist resin to proceed by using a product formed by a photochemical reaction during the exposure process as an acid catalyst, thereby locally changing the solubility of only the exposed portion of the resist resin in a developing solution. Also, U.S. Pat. No. 7,009,148 discloses that a post-exposure bake process is performed by scanning a substrate with a laser.
As disclosed also in U.S. Patent Application Publication No. 2009/060686, the conventional post-exposure bake process has been performed by placing an exposed substrate on a hot plate controlled at a predetermined heating temperature for a predetermined period of time. The heating temperature of the hot plate in a typical post-exposure bake process is approximately 130° C.
As pattern dimensions have become finer in recent years, it has been contemplated to minimize a diffusion length for which acid generated in a resist film during a pattern exposure process is diffused in a post-exposure bake process. General techniques for minimizing the diffusion length are to decrease a processing temperature in the post-exposure bake process and to shorten processing time for the post-exposure bake process. However, the decrease in processing temperature causes the post-exposure bake process itself to be susceptible to environmental effects, thereby giving rise to an apprehension that the temperature uniformity of a substrate deteriorates.
In addition, the decrease in processing temperature causes non diffusion of the acid, as a result, the formation of the photoresist pattern might become incomplete.
For this reason, it is desirable to shorten the processing time for the post-exposure bake process. However, when a substrate is placed on a hot plate and heated, it takes at least 30 seconds or more for the temperature of the substrate to reach an intended heating temperature. Thus, there is a limit to the shortening of the processing time. When an attempt is made to shorten the processing time beyond the limit, there arises a problem such that the dimension accuracy also decreases.
In the post-exposure bake process using the laser as disclosed in U.S. Pat. No. 7,009,148, a region irradiated with the laser is limited. It is hence difficult to process the entire surface of the substrate at a time, but it is necessary to scan the substrate with the laser. This produces a time difference between a start position and an end position for the post-exposure bake process to cause a problem in nonuniform pattern dimensions. Also, the need for scanning increases the processing time to result in an apprehension about the reduction in throughput.